The present invention relates to the manufacturing of torsion cords and improved torsion cords that are used in the suspension of many vehicles, and more particularly to a new and improved method for manufacturing improved torsion cords at a lower manufacturing cost.
Torsion cords have been utilized in the axle suspension system of light duty trucks and recreation vehicles for several decades. Users must be assured that these torsion cords possess stringent physical properties, such as a closely held modulus range, and an extremely low compression set that are difficult to hold and produce competitively by means of conventional molding methods. A limited number of molders have provided torsion cords that have performed satisfactorily, but not without the need for improved production control and efficiency. It is therefore highly desirable to provide a new and improved method and apparatus for manufacturing torsion cords and improved torsion cords made in accordance therewith.
Torsion cords are made of natural or synthetic polyisoprene polymer that is blended with various ingredients to formulate a vulcanite. Polyisoprene is tough and generates heat rapidly during process mastication which can adversely affect the final properties of the torsion cords. Furthermore, the addition of processing oils, etc. that are commonly used to reduce heat and improved blending, is restricted. Thus, it is highly desirable to provide a new and improved method and apparatus for molding torsion cords. It is also highly desirable to provide a new and improved method and apparatus for molding torsion cords that will reduce the number of process functions. It also highly desirable to provide a new and improved method and apparatus for molding torsion cords that will reduce the process costs.
Torsion cords are vulcanized (cured), by the application of heat while the material is confined under pressure for a designed interval, all of which is correlated with a chemically formulated cure system. In the use of the prior molding apparatus and methods used for molding torsion cords, it is essential to economize by curing at the highest possible temperature to reduce the cure cycle time. Consequently, at these extreme limits, strict control of the rubber chemistry, the mixing, and the molding processes are imperative in order to obtain the modulus and compression set specifications. Therefore, it is highly desirable to provide a new and improved method and apparatus for molding torsion cords which will more efficiently provide an improved torsion cord. It is also highly desirable to provide a new and improved method and apparatus for molding torsion cords which allows for curing at moderate conditions. It is also highly desirable to provide a new and improved method and apparatus for molding torsion cords which will allow torsion cords to be manufactured within specified modulus and compression set tolerances more consistently.
Prior torsion cords are limited in length because of the molding equipment. These torsion cords are molded in 36 inch square two-part molds, each part having multiple cylindrical cavities 31.5 inches in length which comprise one-half the molded part. The plates are mounted in a 600 ton hydraulic press which vertically separates the plates while loading the raw material and unloading the molded product. Historically, because of these mechanical limitations, torsion cords have been provided in maximum lengths of only about 31 inches. Thus, torsion cords are available in the marketplace which are either 31 inches in length, or subsequently cut to fractions thereof to accommodate a variety of actual loads. In many instances, to meet a specified spring rate, the 31 inch torsion cord is cut to lengths which result in excessive waste. Therefore, it is highly desirable to provide a new and improved method and apparatus for making torsion cords in which torsion cords can be manufactured in a variety of lengths. It is also highly desirable to provide a new and improved method and apparatus for making torsion cords in which the torsion cords can be manufactured in any desired length to effect economy. It is also highly desirable to provide a new and improved method and apparatus for making torsion cords in which torsion can be manufactured at lengths longer than 31 inches.
The manufacturing of torsion cords in the past has had all of the limitations of any molding process utilizing molds which must be filled, closed and clamped during curing and when open, require the removal of parting line flash from the molded product. It is therefore, highly desirable to provide a new and improved method and apparatus for making torsion cords which have no parting line, no parting line flash, and none of the physical limitations of a conventional clamping system.
It is also highly desirable to provide a new and improved method and apparatus for making torsion cords which does not utilize conventional molding processes. It is also highly desirable to provide a new and improved method and apparatus for making torsion cords that can be easily developed into an automatic process.
Prior compression processes for molding torsion cords inherently presents difficulty in maintaining accurate closure dimensions that are caused by press equipment wear, mold damage, and raw material weight variances. Although, not preferred, diametral tolerances of .+-.0.013 must be expected. It is therefore highly desirable to provide a new and improved method and apparatus for making torsion cords in which diametral tolerances of .+-.0.005 inches can be easily held independent of auxiliary equipment and raw material preparation. It is also highly desirable to provide an improved method and apparatus for making torsion cords in which diametral tolerances of .+-.0.005 inches can be easily held without any parting line flash, and none of the physical limitations of conventional clamping systems.
Prior torsion cord molding processes need expensive tools and equipment. Molds costing up to $10,000 are needed for each product diametrical size. Large presses, a mixing mull, an extruder and cutting equipment in which another $500,000 to $600,000 investment is required, together with the cost of six workers per shift in direct labor. In addition to this, energy, maintenance, insurance, and floor space must enter into the manufacturing cost. It is therefore highly desirable to provide a new and improved apparatus and method for manufacturing torsion cords which requires less manpower, less tangible costs and lower capital investment.
Finally, it is highly desirable to provide a new and improved apparatus and method for making torsion cords and an improved torsion cord which possesses all of the above features.